Characterisation of a  -Lactamase Obtained from a Strain of Bacteroides Fragilis Resistant to  -Lactam Antibiotics

Abstract

SUMMARY The minimum inhibitory concentration of six antibiotics for ten clinical isolates of Bacteroides fragilis was determined. One of the isolates, which was unusually resistant to ampicillin and cephaloridine, possessed an intracellular β-lactamase. This enzyme, which was more active against cephaloridine than against the penicillins, was characterised. No β-lactamase activity could be detected in any of the moderately resistant strains, or in whole-cell preparations, or culture filtrates. The production of β-lactamase was not induced in resistant or sensitive strains by growth in media containing ampicillin. The above evidence supports the view that strains of B. fragilis that are highly resistant to β-lactam antibiotics owe this property to the presence of an intracellular β-lactamase. Attempts to transfer antibiotic resistance from B. fragilis to Escherichia coli and vice versa, and from one strain of B. fragilis to another, were unsuccessful.